1. Field of the Invention
The present invention relates to a security system and method, and more particularly, to a security system and method that perform security and monitoring using measurement of acoustic field variation.
2. Discussion of Related Art
Security systems have been studied for a long time. There are conventional security systems using a security camera scheme, an infrared ray (IR) scheme, an ultrasonic scheme, and a sound measurement scheme.
There is a conventional ultrasonic scheme in which when there is no intrusion, an ultrasonic wave has a waveform having an upper portion and a lower portion that have the same form, and when there is an intrusion, the waveform is distorted. In this case, the distorted waveform is subjected to digital processing and integral operation. A determination is made as to whether there is an intrusion based on a distortion degree of the waveform. The ultrasonic scheme uses a simple principle and employs a waveform transducer to send an ultrasonic wave, which is returned to the waveform transducer for processing. Thus, the ultrasonic scheme can be easily implemented.
The ultrasonic scheme uses an ultrasonic wave and has low efficiency of generation of the ultrasonic wave to air, causing high power consumption. Where a waveform of a generated ultrasonic wave is initially distorted due to an existing object or condition in a certain space, an intrusion signal is generated irrespective of whether there is an intrusion. Measurement in a wide space is limited due to excellent directivity of the ultrasonic wave, and nonuniform reflection of the ultrasonic wave from ambient objects makes an initialization difficult.
There is another conventional scheme that is similar to the above ultrasonic scheme but is applicable only to the inside of a car. This scheme proposes an ultrasonic-wave intrusion detection and alarm system and method for a car capable of digitally modulating an ultrasonic wave, reducing erroneous detection caused by an echo or external noise, and improving the precision of detection. In an initialization process, an initialization is performed through an accumulated amount of data.
This scheme has overcome the limitation of measurement in wide spaces of the ultrasonic wave by limiting its application to the inside of the car. However, since the scheme uses a similar principle to the foregoing scheme, the scheme has a problem of power inefficiency due to use of the ultrasonic wave and has a disadvantage in that an intrusion signal is erroneously generated irrespective of whether there is an intrusion when a waveform of the ultrasonic wave is initially distorted by an existing object or condition in a certain space.
There is another monitoring scheme for determining whether there is an abnormality in a place to be monitored using environmental sound generated according to an environment of the place. A microphone is disposed at the place to be monitored, a feature extractor extracts a given feature from a sound signal from the microphone, and an abnormality determiner compares the extracted feature with an environmental sound reference model stored in a memory to determine whether there is an abnormality in the place. When it is determined that there is an abnormality, an alarm output unit generates an alarm signal and provides the alarm signal to a monitoring person.
In the conventional schemes, since learning is performed under a silent environment at the time of initialization or at a certain sound state, an operation is very sensitive due to an ambient noise after initializations through learning. Accordingly, a malfunction is highly likely to occur when ambient noise other than an intrusion is generated. Further, since very silent intrusion by a person or object causes no variation of environmental sound, the intrusion is not detected.